PROJECT SUMMARY Following their treatment, young adult cancer survivors (YACS) are at increased risk for psychological adjustment problems, including Posttraumatic Stress Disorder (PTSD), a psychiatric disorder characterized by re-experiencing, avoidance, mood and cognitive symptoms following a traumatic event. PTSD is a chronic debilitating disorder affecting as many as 20% of YACS, with significant negative impact on their emotional health, quality of life, and employment, even many years after treatment completion. Despite this significant burden, many YACS with PTSD are not identified and treated, principally because validated assessment methods are not available for this group. Identifying PTSD in YACS is complicated by the overlap of PTSD symptoms with symptoms of other psychiatric disorders, normal developmental challenges, and medical late- effects of cancer treatment, and because PTSD symptoms may not appear for months or years after cancer treatment. Several self-report symptom checklist measures have been developed to identify individuals with PTSD, but these have not been well validated in YACS. Moreover, all major PTSD assessment measures were recently revised following the introduction of a new Diagnostic & Statistical Manual for Psychiatric Diagnoses (DSM-5) in 2013. Consequently, all studies of PTSD in cancer survivors to date used PTSD measures that are now obsolete. This significant revision of PTSD criteria and measures provides a critical opportunity to improve both research and clinical care of YACS with PTSD, but only if these new measures are empirically validated. To address this need, we propose to validate several recently revised PTSD checklist measures in a sample of 250 YACS. Using an interviewer administered Structured Clinical Interview for DSM Disorders (SCID) as a ?gold standard,? the validity of the revised PTSD Checklist (PCL-5), the Posttraumatic Diagnostic Scale (PDS- 5), and the Primary Care PTSD Screen (PC-PTSD) will be assessed. Prior versions of the PCL and PDS have been widely used in cancer survivors, and the 4-item PC-PTSD has been applied across medical settings, but these measures have never been validated against a psychiatric interview in YACS. Following recommendations from the National Center for PTSD we will examine validity of these measures for identifying YACS with PTSD diagnoses, and for identifying those with Partial PTSD (P-PTSD), defined as significant symptoms of PTSD without a PTSD diagnosis, a condition widely reported in cancer survivors. The primary aim is to investigate validity of the newly revised self-report PTSD measures (PC-PTSD, PCL-5 & PDS-5) compared to the SCID, and determine optimal criteria to identify YACS with PTSD and P-PTSD. Secondary aims will be to determine if PTSD and P-PTSD are associated with impaired quality of life in YACS and to explore how novel brief symptom burden and impairment measures can be used to improve the accuracy of PTSD checklist measures in YACS. Findings will have immediate implications for investigators studying PTSD in YACS, and for clinicians evaluating and treating YACS for psychological late-effects of treatment.